Transplanting brown fat for weight loss? It could happen

For those of you struggling with your weight, here’s a future transplant list you will want to be on: Receive some brown fat from a lean, healthy donor, have it injected in or around your belly fat, and quickly see your metabolic function improve, your white-fat deposits make way for lean muscle and your scale show a downward trend.

That tantalizing prospect for fighting fat took a small step closer to reality Monday with the publication of a study that found that, in chubby mice, at least, such as procedure worked.

The study, conducted at the Joslin Diabetes Center in Boston, explored whether it’s possible to boost a body’s stores of brown fat -- the mitochondria-rich fat tissue that burns up lots of calories to keep us warm in cold weather -- as an aid to weight loss. It was published in the Journal of Clinical Investigation.

More specifically, the researchers sought to discover how a body would respond to the transplantation of brown fat from a someone else’s body: Would it be rejected? Would it be assimilated and converted into its unhealthy cousin, white fat? If it “took” inside its new host, would transplanted brown fat behave the way it is designed to act in those who are born with plentiful stores of it -- helping the body to rev higher, burn more calories and clear the bloodstream of excess glucose.

To find the answer, the scientists took a tiny sample -- either .1 gram or .4 gram--of brown fat tissue from the space between a mouse’s shoulders, where it is commonly found. They transplanted it into the visceral cavity of one group of 12-week-old mice made fat by feeding them a high-fat, high-calorie diet, right on top of the animals’ own pad of abdominal fat. Two comparison groups of mice got “placebo” treatments of sorts: They either had a small glass bead transplanted into their belly or a .1-gram bit of white fat.

Eight weeks after the brown fat had been transplanted to the chubby mice, scientists found it had insinuated itself into the fat tissue of its new host and gone to work: the glucose tolerance of the brown-fat transplant patients had improved dramatically compared with the two control groups, and insulin resistance improved, although it grew steadily worse in the two other groups.

By 12 weeks after the brown-fat transplants, these mice ate the same diet -- no more, no less -- but compared with the other groups, they weighed less and their bodies burned more calories. And their total lean mass -- muscles and bones -- was unchanged.

To their surprise, the scientists noted that the improvements they saw in glucose use was not in the muscles of the recipient mice. Instead, the heart, as well as the host’s white fat and brown fat, got better at glucose uptake. The study also suggests that to pack its fat-burning punch, the newly transplanted brown fat cells must work together with the host body’s interleukin-6, a messenger protein made by the immune system but known to play a key role in metabolism.

When it comes to biomedical treatments, it’s a long road from mouse to man. But it may not be too early to ask your lean friends and family members whether, when the time comes, they might have a little brown fat they could spare.

[For the record, 1:25 p.m. Dec. 14: This post originally said that the Joslin Diabetes Center was part of Harvard University Medical Center. There is no such institution. The diabetes center is affiliated with, but not part of, Harvard Medical School.]

[For the record, 2:50 p.m. Dec. 14: the first paragraph of the post mistakely referred to the source of the brown fat as the “recipient” instead of the “donor.”]